In the semiconductor industry, there is a continuing trend toward high device densities. To achieve these high device densities, small features on semiconductor wafers are required. These features include source regions, drain regions, and channel regions that relate to devices, such as field effect transistors (FETs).
In the process of scaling down complementary metal oxide semiconductor (CMOS) devices, which are a type of FET, a vertical dimension must be reduced at the same time as horizontal dimensions are reduced. In particular, in order to avoid short channel effects, source and drain regions, or at least source/drain extension regions adjacent the channel, must be made extremely shallow with a corresponding increase in dopant density to avoid excessive resistance. The formation of ultra-shallow junctions, that is, junctions having source/drain regions no more than about 35 nm thick and with a dopant concentration not less than 5×1019 atoms/cm3, is considered one Of the significant challenges in manufacturing the next generation of CMOS devices. The usual approach to forming source/drain regions is ion implantation. In the conventional approach, following implantation, the substrate is typically annealed to repair the lattice damage and activate the dopants. Such conventional anneal processes result in a modest amount of diffusion.
A process that limits diffusion and results in higher than equilibrium dopant activation is solid phase epitaxial re-growth (SPER). SPER involves re-crystallizing an amorphous doped region at a relatively low temperature, wherein the resulting dopant profile is close to the implanted profile, with little dopant diffusion occurring during the re-crystallization process.
While SPER of amorphous doped regions is effective in forming shallow implants with high dopant concentrations, there are obstacles to its implementation. The main concern is that end-of-range defects form in the region where re-crystallization begins. These defects, which are thought to involve interstitial silicon atoms, increase reverse bias leakage (and thereby increase Off-State current). Thus, there remains an unsatisfied need for effective methods of forming ultra-shallow junctions.